Tone signaling techniques such as “Dual Tone Multi Frequency” (“DTMF”) signaling are known and have been in use with telephone networks for at least the past twenty years. The advent and expanded use of packet switched telephony has presented certain barriers to the use of tone signals. In certain situations, encoders used to encode human speech may alter the frequency composition of a tone to the extent that that tone is not recognized by the device to be signaled. In another case, an encoder may alter the tone such that the device to be signaled mistakes the tone for another or may mistake the tone for two or more tones.
DTMF Relays have been introduced in order to overcome this problem. The DTMF Relay is composed of a DTMF tone Detector and a DTMF tone Generator. The Detector monitors the incoming audio signal and upon detection of a signaling tone produces a control signal instructing the Generator in the receiving station to produce the signaling tone. Unfortunately, the detection of a signaling tone is time consuming and the relay path is sometimes delayed with respect to the voice path such that the signaling tone is detected twice at the receiving station. This is known as double-digit detection. It has been suggested to mute the voice path after the signaling tone is detected, however due to the time intensive nature of the detection process the muting of the voice path is delayed and some residual DTMF signaling is carried by the voice path to the receiving station causing double-digit detection.